DIFFERENTIAL EXPRESSION OF HORSE ESTs IN NORMAL AND SEPTIC FOALS

¹ Department of Environmental and Population Health, Tufts University School of Veterinary Medicine, North Grafton, MA 01536

² Department of Clinical Sciences, Large Animal Hospital, Tufts University School of Veterinary Medicine, North Grafton, MA 01536

Very little is known about the molecular basis of septicemia in the neonatal foal, the most common cause of death in the first 7 days of life. Despite increased awareness of risk factors for sepsis and advances in medical management for critically ill foals, mortality of septic foals remains high. To begin to understand the molecular mechanisms associated with susceptibility to sepsis and the individual differences in response to treatment for sepsis, an analysis of the differential expression of expressed sequence tags (ESTs) previously isolated from a septic Thoroughbred foal was initiated. Blood samples were collected from foals presented to Tufts University Large Animal Hospital and used for extraction of total RNA. Foals were grouped as 0=healthy (n=3), 1=non septic/mildly ill (n=5), 2= septic/very ill (n=12). Differential mRNA expression of 7 ESTs (MHC Class II DQ alpha chain, granulocyte colony-stimulating factor receptor, complement C5a receptor, cell adhesion molecule GMP 140, LY6H protein-lymphocyte antigen, interleukin-1 receptor antagonist, and c-fms protooncogene) known to be involved in cell signaling/cell communication and cell/organism defense was examined in the RNA from septic and non-septic foals. Target gene expression was normalized to beta-2-microglobulin expression using real time RT-PCR. ANOVA results considering all 3 groups separately showed significant effect of gene (P<0.001) and health status (P<0.018) but there were no significant differences in the interaction of gene and health status. There was a significant correlation (P<0.05) between the expression of five of the genes (GCSF receptor, IL1ra, LY6H lymphocyte antigen, and complement C5a receptor) and the foal's white blood cell count. Preliminary results using the stallions of the international reference mapping family indicate that IL1ra, LY6H and c-fms protooncogene are polymorphic, work is underway to test polymorphism status of the other genes. Further work must be done with a larger sample size using RT-PCR analysis of genes suspected to be involved in the events that lead to the septic condition or the individual's positive or negative response to medical treatment. Knowledge of these molecular events in neonatal foals may one day help to prevent sepsis in the genetically predisposed and/or create individualized therapies for this condition.